The present invention relates generally to water valves, and more specifically to an apparatus for reducing the noise generated by the flow of water through water valves used in household appliances such as dishwashers, icemakers and clothes washing machines.
Electrically operated water valves are commonly used in many household appliances such as dishwashers, clothes washers, and refrigerator icemakers. Such appliance water valves are generally controlled by a controller included in the appliance, thereby alternatively turning a water supply on and off as determined by the appliance programming. Such valves also generally include a flow control device which provides a constant water flow rate for all water supply pressures that can be reasonably anticipated. Such flow control devices generally comprise a flexible flow control washer supported by a rigid support. The flow control washer includes a flow control orifice communicating with an aperture in the support. The flow control washer is shaped so that water pressure forcing it against the support causes the flow control orifice to become smaller as the water pressure increases.
Such flow control devices tend to cause noise as the water flows through the valve. Noisy valves are undesirable, especially when used in appliances such as dishwashers and icemakers which operate within the living space of the home. These type of valves can be quite noisy at certain pressures and quiet at other water pressures.
One of the major sources of noise in the operation of an appliance water valve is "cavitation" of the water. Cavitation is the sudden formation and collapse of low-pressure bubbles in a liquid, such as water, as the liquid flows from an area of higher pressure to an area of lower pressure. As the low-pressure bubbles collapse, energy is released which causes structural vibrations within the appliance water valve. Such structural vibrations generally result in the production of noise.
In addition to noise, the structural vibrations due to cavitation may also cause damage to the appliance water valve. In particular, the components within the appliance water valve may be eroded, fatigued, or pitted due to cavitation. Hence, the operative life of the appliance water valve may be reduced by cavitation.
It has been determined that one of the major sources of cavitation is the pressure drop associated with the flow control device. As the flow control pressure drop becomes significant, especially at high water inlet pressures, the pressure on the outlet side of the flow control drops below the vapor pressure of the water and cavitation can occur. The noise generated by cavitation may be lessened by controlling the pressure drop across the flow control device.
One way to control the pressure drop across the flow control device is to create backpressure within the valve. Backpressure may be created a number of ways internal to the valve; however, if excessive backpressure is created, the water flow rate may change from the desired amount and may create an undesirable performance in the appliance. This is particularly of concern at low inlet water pressures.
What is needed therefore, is an appliance water valve which controls the pressure drop through the flow control, thereby reducing cavitation and the noise generated therefrom, but does not impede the flow rate of the water flowing therein. The apparatus must be capable of controlling the pressure drop at steady-state water flow conditions as well as in transient flow conditions and must be capable of operating at a wide range of water inlet temperatures.